The manufacturing of integrated circuits has been significantly improved by the development of new low dielectric constant organic materials (.di-elect cons.=4 or less) which are easily etched in oxygen environments. These new organic dielectrics can withstand temperatures in excess of 300.degree. C. without degradation. Thus, they are highly suitable for use in back-end-of-the-line (BEOL) processing.
In order to pattern low dielectric constant organic materials, the etch rate of any resist applied thereto must be less than that of the low dielectric constant organic material. However, since the etch rates of the low dielectric constant organic materials and prior art resists are substantially the same in oxygen etching ambients, inorganic hard masks, i.e. caps, such as Si.sub.3 N.sub.4, SiO.sub.2 and silicon oxynitride are generally employed to improve the etch rate (i.e., to allow the use of more aggressive etch environments while achieving a selective etch).
The inclusion of a hard inorganic mask layer introduces several complexities into the integrated circuit fabrication process. For one thing, the hard mask layer must be patterned to match the pattern of the photoresist layer prior to patterning the low dielectric constant organic material.
A second problem associated with the use of an inorganic hard mask layer is that the dielectric constant of such materials are high (on the order of 7.0 or higher). As such, the inclusion of a hard inorganic mask layer increases the overall dielectric constant of the resultant film stack. Thus, the inclusion of a hard inorganic cap serves to defeat the purpose of utilizing the organic dielectric layer in the first place, i.e. reduction of the dielectric constant of the film stack.
Yet a third problem associated with the utilization of a hard inorganic cap layer is that, if the organic dielectric is employed as a sacrificial template (e.g., for copper wiring), it is necessary to eliminate the hard masking material before the organic dielectric can be removed after the templating function has been performed.
Attempts have been made in the prior art to overcome the aforementioned problems associated with the use of a hard inorganic cap layer. One such method, commonly employed in the art, is the removal of the hard inorganic cap layer by reactive ion etching (RIE). Unfortunately, such RIE processes typically employ fluorine-containing compounds as the active species. Fluorine-containing compounds not only remove the thin hard inorganic cap layer, but tend to etch the organic dielectric layer and thus reduce pattern fidelity in the lateral direction.
A further expedient employed to remove the hard inorganic cap layer is the utilization of a wet etch. Wet etches, which typically use hot phosphoric acid as an etchant, are not compatible with copper wiring found in many BEOL applications. Furthermore, wet etches often provide isotropic etching which may create undercuts in the patterned regions.
In view of the above identified problems associated with hard inorganic cap layers, there is a need to provide a new method which can be used to pattern low dielectric constant organic materials which eliminates the use of a hard inorganic cap layer in the patterning process.